Vapor degreasing and solvent cleaning with fluorocarbon based solvents have found widespread use in industry for the degreasing and otherwise cleaning of solid surfaces, especially intricate parts and difficult to remove soils.
In its simplest form, vapor degreasing or solvent cleaning consists of exposing a room temperature object to be cleaned to the vapors of a boiling solvent. Vapors condensing on the object provide clean distilled solvent to wash away grease or other contamination. Final evaporation of solvent from the object leaves behind no residue as would be the case where the object is simply washed in liquid solvent.
For difficult to remove soils where elevated temperature is necessary to improve the cleaning action of the solvent, or for large volume assembly line operations where the cleaning of metal parts and assemblies must be done efficiently and quickly, the conventional operation of a vapor degreaser consists of immersing the part to be cleaned in a sump of boiling solvent which removes the bulk of the soil, thereafter immersing the part in a sump containing freshly distilled solvent near room temperature, and finally exposing the part to solvent vapors over the boiling sump which condense on the cleaned part. In addition, the part can also be sprayed with distilled solvent before final rinsing.
Vapor degreasers suitable in the above-described operations are well known in the art. For example, Sherliker et al. in U.S. Pat. No. 3,085,918 disclose such suitable vapor degreasers comprising a boiling sump, a clean sump. a water separator, and other ancillary equipment.
Cold cleaning is another application where a number of solvents are used. In most cold cleaning applications the soiled part is either immersed in the fluid or wiped with rags or similar objects soaked in solvents and allowed to air dry.
Fluorocarbon solvents, such as trichlorotrifluoroethane, have attained widespread use in recent years as effective, nontoxic and nonflammable agents useful in degreasing applications and other solvent cleaning applications. Trichlorotrifluoroethane has been found to have satisfactory solvent power for greases, oils, waxes and the like. It has therefore found widespread use for cleaning electric motors, compressors, heavy metal parts, delicate precision metal parts. printed circuit boards, gyroscopes, guidance systems, aerospace and missile hardware, aluminum parts and the like.
The art has looked towards azeotropic compositions including the desired fluorocarbon components such as trichlorotrifluoroethane which include components which contribute additionally desired characteristics, such as polar functionality, increased solvency power, and stabilizers. Azeotropic compositions are desired because they exhibit a minimum or maximum boiling point and do not fractionate upon boiling. This behavior is desirable because in the previously described vapor degreasing equipment with which these solvents are employed. redistilled material is generated for final rinse-cleaning. Thus, the vapor degreasing system acts as a still. Unless the solvent composition exhibits a constant boiling point. i.e., is an azeotrope or is azeotrope-like, tractionation will occur and undesirable solvent distribution may act to upset the cleaning and safety of processing. Preferential evaporation of the more volatile components of the solvent mixtures, which would be the case if they were not an azeotrope or azeotrope-like, would result in mixtures with changed compositions which may have less desirable properties, such as lower solvency towards soils, less inertness towards metal, plastic or elastomer components, and increased flammability and toxicity.
The art is continually seeking new fluorocarbon based azeotropic mixtures or azeotrope-like mixtures which offer alternatives for new and special applications for vapor degreasing and other cleaning applications. Currently, of particular interest, are such azeotrope-like mixtures which are based on fluorocarbons which are considered to be stratospherically safe substitutes for presently used fully halogenated chlorofluorocarbons. The latter are suspected ot causing environmental problems in connection with the earth's protective ozone layer. Mathematical models have substantiated that hydrochlorofluorocarbons, such as 1,1-dichloro-1-fluoroethane (FC-141b), will not adversely affect atmospheric chemistry, being negligible contributors to ozone depletion and to green-house global warming in comparison to the fully halogenated species.
We are aware of only one disclosure of an azeotropic composition including 1,1-dichloro-1-fluoroethane, namely Anon., Research Disclosures, Vol. 162, p. 70 (1977) in which it is stated that n-pentane and iso-pentane form binary azeotropes with 1.1-dichloro-1-fluoroethane.
U.S. Pat. No. No. 3,936,387 discloses the azeotropic composition of methanol with 1,2-dichloro-1-fluoroethane, FC-141, which is an isomer of FC-141b. Similarly, U.S. Pat. No. 4,035,258 discloses the azeotropic composition of ethanol with 1,2-dichloro-1-fluoroethane. This information did not lead us to the azeotropic composition of the invention since, as is well known in this art, there is no published, reliable basis on which to predict azeotropy. Moreover, as is equally well known, the existence of an azeotropic composition does not enable one skilled in the art to predict azeotropy between or among related components. For example, U.S. Pat. No. 3,936,387 discloses that FC-141 and isopropanol form an azeotropic composition, whereas FC-141b and isopropanol do not form an azeotrope.
Nitromethane is a known stabilizer for preventing metal attack by chlorofluorocarbon mixtures containing alcohols. For example, U.S. Pat. No. 3,573,213 discloses an azeotropic mixture of 1,1,2-trichloro-1,2,2-trifluoroethane with nitromethane in which mixture nitromethane is stated to perform such stabilizing function.
It is accordingly an object of this invention to provide novel azeotrope-like compositions based on FC-141b which are liquid at room temperature and which will not fractionate under the process of distillation or evaporation, which are useful as solvents for use in vapor degreasing and other solvent cleaning applications including defluxing applications. Another object of the invention is to provide novel environmentally acceptable solvents for use in the aforementioned applications.